Study On 64 Slice CT Low Dose Chest Scanning Scheme

Objective:This research aims to compare the effects on the image quality with conventional dosage chest CT scanning over low dose chest CT scanning technology, in order to explore a more reasonable lower thorax dosage scanning scheme. Method:To break the patients into 2 groups. For the first group (Group A), select the tracheal carina horizontal scan, range 3.2cm, with 200mA,100mA,50mA, 25mA treat respectively, other conditions remains unchanged. For the second group (Group B), keep the scanning position and method as the same as Group A, with automatic mA but differentiate the noise index of 9.2,15,20,25,30 respectively, other conditions remaining unchanged. In the end, the patient's data such as DLP, CTDIvol, noise index, CNR were objectively analyzed, meanwhile then the lung window, mediastinal window were scored subjectively. Results indicates:for the first group:200mA CT image quality subjective scoring good, mediastinal window and lung window is 6; 100mA mediastinal window 5.2 score, lung window 5.85 score; mediastinal window 50mA score is 4.3 points, lung window 5.04 score; mediastinum windows 25mA 3.3, lung window is 4.22 points. Noise index increased with mA reducing. Noise of 200mA and 100mA are similar,50mA noise increases, and reach highest with 25mA. While DLP, CTDIvol, CNR with mA reduced significantly decreased 50mA, the image quality is acceptable, and the 200mA compared to the DLP about 13%. Second kinds of methods:noise index of 9.2 and CT image quality subjective scoring 15, lung window and mediastinal window scores in 6; noise index of lung window score of 20 to 6, mediastinal window score was 5.71; the noise index of lung window score of 25 to 5.86, scoring 4.8 in mediastinal window the noise index; lung window score of 30 to 5.39, scoring 4.08 in mediastinal window. Various scanning of CT lung window images and mediastinal window image quality subjective scoring as the noise increases, the quality is slightly lower, mediastinal window decreased obviously, CNR also decreased, but DLP, CTDIvol with the noise decreases obviously. The noise index of 30 image quality is acceptable, the DLP is about 46% at the level of 9.2 of noise index. This study Conclude that:either to reduce the tube current to 50mA with other condition remaining unchanged in the conventional method, or rise noise index tolerance to 30 in the conventional method, can meet the need of clinical diagnosis requirement with significant reduction of radiation dosage to the patients.